The contract to supply Eurofighter's propulsion system was awarded to EuroJet Turbo GmbH in 1986. EuroJet is a consortium of companies from each partner nation and after workshare changes; Rolls-Royce of the UK has 36%, MTU (Motoren-und Turbinen-Union) of Germany has 30%, FiatAvio of Italy has 20% and ITP (Industria de Turbo Propulsores) of Spain has 14%. The partnership has resulted in the EJ200 advanced turbofan and associated management systems.

EuroJet 200

Origins and Technology

The EJ200 started life in 1982 as the Rolls Royce/British MoD XG-40 Advanced Core Military Engine or ACME demonstrator. This programme, split into three phases; technology (1982-88), engine (1984-89) and assessment (1989-95) developed new fan, compressor, combustor, turbine (including high temperature life prediction) and augmentor systems using advanced materials and new manufacturing processes. The first full engine commenced rig testing in December 1986 with the final XG-40 running for some 200 hours during 4000 cycles bringing the programme to a close in June 1995.

Upon formation of the EuroJet consortium in 1986 much of the continuing XG-40 research was used for the new programme. The requirements were for a powerplant capable of higher thrust, longer life and less complexity than previous engines. The result was a powerplant with similar dimensions to the Tornado's RB199 yet having almost half as many parts (1800 against 2845 for the RB199) and delivering nearly 50% more thrust. A very noticeable difference between the two engines can be seen by comparing the turbine blade designs. Compared to the RB199 the EJ200's blades are enormous and show leanings towards sustained transonic and supersonic flight profiles.

Cross section of rotor blades

Single Crystal Turbine Blades

On the microscopic scale all metals (and their alloys) are an arrangement of crystals. How these crystals are arranged, their size and distribution depends on what the metal or alloy is and how it was forged.

The vast majority of turbine blades are now made from a Nickel or Titanium based super-alloy. The alloy will contain a variety of elements (their amounts are typically proprietary and well guarded!) such as Tungsten, Cobalt, Chromium, etc. The resulting material is extremely hard and difficult to machine and thus blades tend to be forged in a process called investment casting. When forged using traditional constant temperature furnaces the blade contains many small precipitates of various compounds (Cobalt, Tungsten, Ni3Al, Ni3Ti, etc.). This resolves certain physical problems with older generation blades (such as problems with power law creep) but unfortunately at high temperatures the blade can still deform irreversibly due to a process known as diffusional creep.

To vastly reduce this creep problem (which is basically caused by the small, random grain structure) a different approach to manufacture is taken in which giant single crystals are grown. This is achieved by using either a special furnace across which a temperature gradient can be applied or by slowly moving the blade mould through the furnace, a process called Directional Solidification. The resulting rotor is very resistant to both diffusional creep and power law creep and thus may be used at higher operating temperatures. Thus the efficiency of the jet engine is improved and it becomes possible to run the engine under more extreme conditions (such as cruising supersonically) for longer.

The EJ200 is an advanced design based on a fully modular augmented twin-spool low bypass layout. The compressor utilises a three stageLow Pressure Fan (LPF) and a five stageHigh Pressure Compressor (HPC). The fan features wide-chord single crystal blade/disc (blisk) assemblies designed for low weight (including the removal of guide vanes), high efficiency operation. The three stages achieve a pressure ratio of around 4.2:1 with an air mass flow of some 77kg/s (or 170lb/s). Like the fan the five stage compressor also features single crystal blisk aerofoils. The use of single crystals and blade/disc units can both bring enormous potential advantages to how the powerplant may be operated (see fact box).

Following the fan/compression stages fuel is injected via an annular combustor designed for low smoke operation. The key factors in determining jet engine efficiency and achievable work are the temperature and pressure differences attained between the engine inlet and combustor outlet. In the EJ200's case the outlet stator temperature is in excess of 1800K with a pressure ratio (achieved in just eight stages) of some 25:1.

Such a high combustor temperature requires special precautions be taken with the High Pressure Turbine, or HPT which is directly downstream. To help reduce this problem the HPT uses air cooled single crystal blades. However there is a limit to what can be achieved using air cooling. In fact it eventually becomes detrimental to use cooling because it adversely effects the achievable combustion temperature and thus reduces efficiency. To overcome this the EJ200's HP turbine blades also utilise a special Thermal Barrier Coating, or TBC. This barrier is comprised of two plasma deposited layers, a special bonding coat over which a top layer of a Nickel-Chromium-Yttrium ceramic material is applied. Although this increases the life of the blade and increases the achievable operating temperature it does require regular inspection to ensure the coating remains viable. Following the single HPT is a further single Low Pressure Turbine (or LPT) stage again employing single crystal blades. In both the HPT and LPT a powder metallurgy disc is employed. A titanium alloy based mono-parametric convergent/divergent (Con-Di) nozzle completes the engine improving achievable thrust while helping to optimise the system for different flight profiles.

Powder Metallurgy

Most metal structures and items are constructed by milling a solid piece of forged material. However over recent years a different method of forming has become possible using powdered metals.

The major benefit of powder metallurgy is that it can produce a component with typically >95% the density of a forged/machined equivalent but at lower cost. The actual procedure used is actually quite straightforward. The metal powder (or combination of blended powders) is compressed under high pressure into a mould of the component to be produced. It may also be possible to incorporate special compounds in the metal powder blend to enhance for example, temperature resistance or aid lubrication. The mould containing the compressed powder mix is then be fired or sintered. Upon cooling the mix crystallises to form a solid component.

The result is a relatively cheap component that can exhibit very similar physical properties to equivalent machined/forged items but at lower cost.

Overall the EJ200 employs a very low By-Pass Ratio (the ratio of air which bypasses the core engine or compressor stages) of 0.4:1 which gives it a near turbo-jet cycle. Such a low BPR has the benefit of producing a cycle where the maximum attainable non-afterburning thrust makes up a greater percentage of total achievable output. At its maximum dry thrust of 60kN (or 13,500lbf) the EJ200's SFC is in the order of 23g/kN.s. With reheat the engine delivers around 90-100kN (or 20,250-22,500lbf) of thrust with an SFC of some 49g/kN.s. Compared to other engines these figures may actually seem relatively high, however such data must be used with caution and evaluated with all other performance data to be of any use. With reheat the engine weighs just 2286lb giving a Thrust to Weight Ratio of around 9:1.

An interesting point to note is that the baseline production engine is also capable of generating a further 15% dry thrust (69kN or 15525lbf) and 5% reheat output (95kN or 21263lbf) in a so called war setting. However utilising this capability will result in a reduced life expectancy.

Much is currently being made about supercruise, that is the ability to cruise supersonically without the use of reheat (afterburn) for extended periods of time. Although never stated explicitly (as for example with the U.S. F-22) the Typhoon is capable of and has demonstrated such an ability since early in its flight program according to all the Eurofighter partnets. Initial comments indicated that, with a typical air to air combat load the aircraft was capable of cruising at M1.2 at altitude (11000m/36000ft) without reheat and for extended periods. Later information appeared to suggest this figure had increased to M1.3. However even more recently EADS have stated a maximum upper limit of M1.5 is possible although the configuration of the aircraft is not stated for this scenario (an essential factor in determining how useful such a facility is). The ability to maintain transonic and supersonic flight regimes without resorting to the use of reheat is achieved mainly thanks to the advanced materials and design of the EJ200. For times when a quick sprint is required the Typhoon can employ reheat with an upper (design) limit of Mach 2.0.

EJ200 development

EJ200 Specification

Length, m (ft,in)

~ 4.0 (~ 13'2")

Diameter, m (ft,in)

~ 0.85 (~ 2'9")

Dry Thrust, kN (lbf)

>60 (>13500)

with Reheat, kN (lbf)

>90 (>20250)

By-Pass Ratio

0.4:1

Total Pressure ratio

25:1

Fan Pressure ratio

4.2:1

Air mass flow, kg/s (lb/s)

77 (170)

SFC dry, g/kN.s

23

SFC reheat, g/kN.s

49

Since the first EJ200 ran in 1991 some 14 development engines have been constructed. The first three plants were for design verification amassing some ~700 hours of bench test time. Another 11 engines were then constructed and placed in Accelerated Simulated Mission Endurance Testing, or ASMET. These prototypes (designated EJ200-O1A) were used to verify the engine design and reliability. During this stage the first two Development Aircraft, DA1 and DA2 entered flight testing. Since the EJ200 had not been certified for flight these first two aircraft were equipped with Tornado ADV class Turbo-Union RB199-104D engines (the D signifies the removal of the thrust reversal buckets). These have have a significantly lower dry thrust, some 42.5kN, than the EJ200 but are approximately the same size. In mid-1998 these RB199's were replaced with EJ200-03A models (see below).

So far over 10000 hours of combined rig testing have been achieved of which some 2800 hours were in altitude testing facilities. In addition the EJ200 has completed well over 650 real flights in the various Development Aircraft from sea level to 15000m (50000ft) and from 135kts through M2.0.

The first Eurofighter to receive the (flight certified) EJ200-01A was the Italian DA3 in 1995 with its first flight in June of that year. The remaining development aircraft also use the EJ200 powerplant (both the EJ200-01A and 01C), but the DA3 remains the primary engine integration aircraft. The DA3 has been used for testing not only the EJ200 itself, but also the Full Authority Digital Engine Control (FADEC) system and Auxiliary Power Unit (APU). In April 1997 EuroJet completed and obtained flight certification on the full pre-production model engine, the EJ200-03A.

In January 1998 EuroJet signed production and production investment contracts with NETMA for some 1500 engines worth around DM12.5B covering the basic order of 620 Eurofighter's. Following this in January 1999 EuroJet received official orders for the first 363 engines to equip the 148 Tranche-1 Typhoon's as well as providing a number of spares. In June 1999 EuroJet obtained flight clearance for the final production standard powerplant with production release scheduled to occur by the end of 1999. The first two production engines were handed over to BAE on the 12th July 2001 at Rolls Royce's Filton plant in Bristol. They were subsequently integrated into IPA1, the first production Eurofighter, at BAE's Warton facility.

Engine Management

The EJ200 is controlled by both an Engine Control Unit and a fuel management system supplied by LucasVarity Aerospace. The primary engine control system developed by ENOSA and Technost SpA under the leadership of Dornier (an DASA company) and Smiths Industries is a Full Authority Digital Engine Control, FADEC unit. Its responsibilities include overall engine management, including afterburn fuel flow and control of the nozzle area.

The third system comprises the Engine Monitoring Unit (EMU) developed by ENOSA, BAE Systems and Microtechnica. Its sole purpose is the self diagnosis of engine faults, it thus augments the structural health monitoring system. The EMU takes its input from both the fuel management and FADEC units as well as a full array of dedicated sensors within the engine.

Future of the EJ200

Engine uprating

The EuroJet consortium were required to build an engine (often referred to as EJ2x0) which had at least a 20% growth potential. There are already plans to carry out the necessary modifications to reach this higher (Stage-1) output in the 2000 to 2005 timeframe. Such an improvement will require a new Low Pressure Compressor (raising the pressure ratio to around 4.6) and an upgraded fan (increasing flow by around 10%). This would result in the dry thrust increasing to some 72kN (or 16,200lbf ) with a reheated output of around 103kN (or 23,100lbf). Given recent increases in the weight of the Typhoon it may not be unexpected to find this upgrade performed in the near future.

More interestingly perhaps is Rolls-Royce and EuroJet's plan to increase the output 30% above the baseline specification as a Stage-2 modification. Such an upgrade will require more substantial plantwide changes including a new LP compressor and turbine and an improvement in the total pressure ratio. These upgrades would yield a new dry thrust of around 78kN (or 17,500lbf) with a reheated output of around 120kN (or 27,000lbf). The indications are that these improvements will come on stream between 2005 and 2010, in time for the Typhoon's Mid Life Upgrade expected around 2016.

Thrust Vectoring Control

Thrust Vectoring

Thrust Vectoring Control became a big issue in the 1980's and early 1990's with the majority of aerospace companies pushing ahead with related programs. There are two basic types of TVC, 2D and 3D. Two dimensional vectoring (2DTVC) works by directing the exhaust up or down (pitch vectoring), the F-22 Raptor features such a system. While three dimensional vectoring (3DTVC) adds the ability to direct the thrust left to right (yaw vectoring).

The are several real benefits to employing thrust vectoring, for example; decreased take-off and landing distances, higher achievable angles of attack, improved control at low speeds/altitudes, reduction in size and number of control surfaces and reduced supersonic drag (by using the vectoring equipment to adjust trim rather than the control surfaces). There are however questions over just how useful TVC will be in future air battles with the increasing move towards beyond visual range engagements.

As well as the potential for increasing the EJ200's thrust there are also plans to incorporate a Thrust Vectoring Control, or TVC nozzle.

The EJ200's TVC nozzle is a joint project lead by Spain's ITP and involving Germany's MTU. Preliminary design of the system began in mid-1995 at ITP, the proceeding years involved work by both ITP and MTU to deliver a fully functional EJ200 integrated system. The outcome of this research led to the first 3DTVC equipped EJ200 undergoing rig trials in July 1998. The nozzle requires relatively few modifications or additions to be made to the EJ200; a new hydraulic pump, reheat liner attachment upgrades, casing reinforcement, new actuators and associated feed equipment. More importantly the equipment fits within the engines current installation envelope and therefore no changes will need to be made to the Typhoon to accommodate the system.

There are essentially three types of vectoring nozzle; ones in which the entire post-turbine section is moved, those which feature external nozzle attachments for directing thrust (e.g. the X-31 paddles) or ones in which thrust is vectored within the divergent section. The ITP system uses the later design requiring no external equipment (which adds weight and offers relatively poor efficiency) and reducing distortion on the major engine structures (a problem with using the first method).

The new Thrust Vectoring Nozzle, TVN is a convergent/divergent type containing three concentric rings linked via four pins forming a unified Cardan joint. Each of these rings serves a purpose, the inner ring is connected to the nozzle throat area with the secondary ring forming a cross-joint connection with the pivoting outer ring. This outer ring is in turn connected to the divergent section (green on the CAD diagram) via several struts or reaction bars (black on the CAD diagram to the left). The outer ring is controlled by either three or four hydraulically powered actuators situated at the North, South, East, West, South West and South East positions. By minimising the number of required actuators (either three or four) ITP claim there is little additional weight, reduced actuator power demands and increased reliability over previous systems. Additionally the nozzle utilises a partial balance-beam effect to minimise the actuator load requirement. This effect uses the exhaust gases themselves to close the nozzle throat area, according to ITP this gives a 15% reduction in actuator loads in certain circumstances.

The baseline vectoring configuration uses three actuators (North, South East and South West). By moving each actuator either in or out the outer ring (red) can be tilted in any direction (see CAD diagram to right, top picture) thus offering both pitch and yaw control. Any net directional movement in the outer ring is then translated via the struts into a larger movement of the divergent section, vectoring the thrust. As well as vectoring control (via movement of each actuator) it is possible to alter the throat area directly by moving all three actuators outward or inward in parallel. In both cases the outer pivot and the inner (green) throat area ring are fixed in the axial direction which reduces the required number of actuators.

Beyond the baseline case the TVN includes a pro-baseline configuration offering the ability to alter the divergent section exit area as well as vectoring thrust and altering the throat area. To achieve this the outer ring is split into top and bottom halves and four actuators (in the N, E, S and W positions) are utilised (see CAD diagram to right, bottom picture). By moving each actuator in a unified/combined manner the thrust can be vectored and the throat area altered. However by moving just the N and S actuators the split ring hinge can be opened and closed. In turn this moves the upper and lower strut series either in or out opening or closing the exit area. In a traditional Con-Di nozzle the exit area is directly related to the throat area. The problem with this approach is that it is extremely difficult to optimise the nozzle shape to different flight profiles, e.g. subsonic cruise, supersonic dash. By allowing dynamic control of the exit area the nozzle shape can be altered on the fly. According to ITP this allows for significant improvements in achievable thrust in all flight profiles.

The three ring system is not the only unique feature of the nozzle. In previous convergent/divergent systems the reaction bars or struts have been connected to the divergent section at a single point. This limits their deflection range thus imposing limits on achievable thrust vectoring (typically to no more than 20°). The ITP TVN however uses a dual point hinged connection allowing a far greater range of movement to be achieved (according to ITP, studies indicate 30°+ can be achieved). By careful placement of the struts, problems with the nozzle petals overlapping or colliding are also removed.

Since rig trials commenced in 1998 the TVC equipped EJ200-01A has run for 80 hours (February 2000) of which 15 hours were at full reheat (including sustained five minute burns) during 85 runs. These trials have included over 6700 vectoring movements at the most severe throttle setting and 600 throttling cycles under the most demanding vectoring conditions. These trials demonstrated full, 360° deflection angles of 23.5° with a slew rate (the rate at which the nozzle can be directed) of 110°/s and a side force generation of some 20kN (equal to approximately to one third of the total EJ200 baseline output). These vectoring trials have included both programmed ramp movements and active joystick control. The studies have also verified the MTU developed DECU (Digital Engine Control Unit) software and FCS connections.

During the summer of 2000 a round of altitude trials commenced at the University of Stuttgart, Germany. These are focused on determining the effects of temperature and pressure variation on the nozzle materials, shape and performance. Additionally ITP are continuing work on further reducing the weight of the system.

In November 2000 ITP announced that an agreement had been reached with Germany and the U.S. to utilise the X-31 VECTOR test aircraft for flight trials of the nozzle. This will see a modified EJ200/TVN combination fitted to the X-31. The modification work required will involve all members of the EuroJet consortium. Additional input is likely from EADS and Boeing as well as NETMA in providing the required EJ200's and equipping the X-31. The Spanish government has agreed to pay for flight certification of the system and provide test pilots. The first flight trials are expected in late 2002 to early 2003. In addition Eurofighter and EuroJet have expressed a desire to commence flight trials of DA1 equipped with the nozzle sometime from 2003. How this fits in with the X-31 test phase is currently unclear.

ITP have suggested that a Eurofighter fitted with the nozzle will benefit in a number of areas including; reduced after body drag (through tighter nozzle shape control), an estimated 7% improvement in installed thrust for the supersonic cruise regime (M1.2 non-reheat at 35000ft) and a 2% improvement in maximum take-off thrust.

At this stage there are no definite plans to fit the nozzle to any production Eurofighter. However Eurofighter, EuroJet and a number of consortium nations and other companies have indicated a desire to include the nozzle (if possible) in Tranche-3 aircraft (due from 2010). This would fit with the stated desire of the four consortium nations to incorporate new technologies in sucessive Eurofighter production runs. The current Eurofighter struture has already been strengthened in anticipation of increased loads created by TVC as well as higher output EJ2x0 series powerplants.

The webmasters would like to express their thanks to ITP R&D for providing the information and material on the 3DTVC nozzle and Rolls Royce for material on the XG-40 and EJ200.